This invention relates to an embossing device and, more specifically, to an embossing device intended for a machine of the tobacco industry, preferably a packaging machine.
The invention also relates to a method for identifying a web of wrapping material in a packaging machine.
A packaging machine designed to make packets filled with tobacco products, such as cigarettes, for example, to which express is made herein without limiting the scope of the invention, comprises an embossing device.
The embossing device embosses a web of wrapping material, usually foil paper or the like, which, after being cut into lengths, is fed to the wrapping system of the cigarette packaging machine.
As is known, in packaging machines of this kind, the web of foil paper is fed by means of an unwinding system along a predetermined path up to a cutting system which divides it along a cutting line transversal to a direction of web feed into individual lengths, each used to wrap a group of cigarettes to form an inner wrapper of a respective packet.
As mentioned, the web upstream of the cutting system is subjected to the action of the embossing device which basically comprises two counter-rotating rollers, a matrix roller and an opposing roller, located on opposite sides of the aforementioned path and tangent to each other.
On their respective cylindrical surfaces, these rollers are provided with protrusions, for example frusto-pyramidal in shape, which give the web passing through it its typical rough-textured surface.
Generally speaking, the cylindrical surfaces of the embossing rollers may also have zones without the frusto-pyramidal protrusions or with protrusions having other shapes, to produce desired graphic patterns or text on each length of web and hence on a portion of the inner wrapper of the cigarette packet.
In order to position the graphic patterns relative to the group of cigarettes, the embossing device is usually shaped to imprint on each length of web a reference mark or centering mark used to synchronize the cutting system with the unwinding of the web.
More specifically, the centering mark, usually also made by embossing, allows both the unwinding system and the cutting system to be synchronized based on the pattern to be imprinted on the web.
The packaging machine comprises a system for reading the mark in order to identify a predetermined section of the web.
The cutting system and the web unwinding system are controlled according to the recognition of that section.
The prior art solutions have some disadvantages.
In the case of uniform embossing, the reference mark consists, for example, of a rectangle which is not embossed.
With other types of background embossing and/or web material, however, it is necessary to optimize the contrast between the reference mark and the background in order to allow it to detected by the optical reading system.
The centering mark may be, for example, in the form of a uniformly embossed rectangle on a non-embossed web or a non-embossed rectangle inside a uniformly embossed frame.
In order to identify and choose the type of mark most easily detected by the optical system, packaging machine constructors have to carry out a number of tests.
Before being able to determine the reference mark specifications, these tests require the construction or purchase of embossers with different patterns and reference marks, a set of measurements and tests and calibration of the optical system.